title: Exogenous melatonin reproduces the effects of short day lengths on hippocampal function in male white-footed mice, Peromyscus leucopus.
abstract: Photoperiodism is a biological phenomenon, common among organisms living outside of the tropics, by which environmental day length is used to ascertain the time of year to engage in seasonally-appropriate adaptations. White-footed mice (Peromyscus leucopus) are small photoperiodic rodents which display a suite of adaptive winter responses to short day lengths mediated by the extended duration of nightly melatonin secretion. Exposure to short days alters hippocampal dendritic morphology, impairs spatial learning and memory, and impairs hippocampal long-term potentiation (LTP). To determine the role of melatonin in these photoperiod-induced alterations of behavioral, neuroanatomical, and neurophysiological processes in this species, we implanted male mice subcutaneously with melatonin or empty Silastic capsules and exposed them to long or short day lengths. After 10 weeks, mice were assessed for hippocampal LTP, tested for spatial learning and memory in the Barnes maze, and morphometric analysis of neurons in the hippocampus using Golgi staining. Extending the duration of melatonin exposure, by short-day exposure or via melatonin implants, impaired both Schaffer collateral LTP in the CA1 region of the hippocampus and spatial learning and memory, and altered neuronal morphology in all hippocampal regions. The current results demonstrate that chronic melatonin implants reproduce the effects of short days on the hippocampus and implicate melatonin signaling as a critical factor in day-length-induced changes in the structure and function of the hippocampus in a photoperiodic rodent.
authors.affiliation: Department of Neuroscience, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA. Electronic address: walton.315@osu.edu.
authors.forename: J C
authors.initials: JC
authors.lastname: Walton
authors.affiliation: Department of Oral Biology, The Ohio State University College of Dentistry, Columbus, OH, 43210, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Oral Biology, The Ohio State University College of Dentistry, Columbus, OH, 43210, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Travers
authors.affiliation: Department of Neuroscience, The Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelson
mesh_terms: D000818:Animals; D056547:CA1 Region, Hippocampal / Q000166:cytology; D003692:Delayed-Action Preparations; D003712:Dendrites; D004343:Drug Implants; D006624:Hippocampus / Q000033:anatomy & histology / Q000166:cytology* / Q000502:physiology; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology*; D008297:Male; D018782:Maze Learning / Q000187:drug effects; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D008568:Memory / Q000187:drug effects*; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010542:Peromyscus; D017440:Photoperiod; D013037:Spatial Behavior / Q000187:drug effects
chemical_list: D003692:Delayed-Action Preparations; D004343:Drug Implants; D008550:Melatonin
keywords: Barnes maze; LTP; hippocampus; melatonin; neuronal morphology; photoperiod